1. Field of the Invention
This invention relates to a seat discomfort preventive device adapted for use in transport vehicles.
2. Description of the Related Art
Conventionally, in the seats of transport vehicles, the angle of inclination of a seat back for supporting the upper part of a passenger or a driver, a seat cushion for supporting the buttocks and thighs, a leg support for supporting the shanks under the condition that the limbs are stretched, etc. is adequately set so as to make a passenger most comfortable. (See, for example, "Collection of commonly known/used techniques", Car Seat, page 195, published by the Japanese Patent Office on Feb. 26, 1988.)
A proper angle of inclination of the seat back will give the sense of comfort to the upper part of the passenger, and a proper angle of inclination of the seat cushion and of the leg support will give the sense of comfort to buttocks and to thighs and shanks, respectively.
However, even if the seat is changed in position to cause a change in the seating posture of the passenger, the sensibility of the passenger and the sensitivity of each physical sense organ adapt quickly to such a change of seating posture and the passenger again undergoes the sense of discomfort.
Furthermore, if the upper part and the head are held virtually horizontal, the vigilance of the sympathetic part of the autonomic nervous system in the body lowers; consequently, the return of blood (controlled by the sympathetic nervous system) from the venous blood vessel of the four limbs (inclusive of the shanks) to the heart tends to stagnate. That is, the adjustment of the seat in terms of the angle of inclination brings about little effects in giving the sense of comfort to the limbs (particularly to the shanks), or rather, aggravates the sense of discomfort of the shanks because the excitation level of the sympathetic nervous system is decreased.
Therefore, even if any conventional reclining mechanism is incorporated for the purpose of improving the sense of seat discomfort, the sense of discomfort is rather aggravated.